1. Field of the Invention
The present invention relates to a method and apparatus for peeling-off a bivalve, which is capable of effectively separating edible parts in a starting bivalve in a raw state from its shell, and to a before-separation heating device. More particularly, the present invention relates to a bivalve peeling-off method and apparatus suitable for effectively separating a ligamnent of a scallop in a raw state from its shell.
2. Description of the Related Art
In general, to remove an edible part from a starting bivalve, e.g., a ligament consisting of an adductor muscle and a shell hinge ligament of a scallop in a raw state from its shell, a thin knife-like tool referred to as a shell opener is used to manually cut the shell-connected part of the ligaments closing two shells of the scallop.
However, when the ligament of the scallop is manually cute and separated from the shell, the following problems are encountered: a problem of a lower efficiency; a problem that a great deal of labour and a lot of time are required; and a problem that when a large number of scallops was landed and in other cases, the freshness of the scallops is lowered, if the scallops are treated quickly by a large number of workers.
Thereupon, various proposals have conventionally been made for the purpose of effectively separating the edible parts of the startinbg bivalves.
These conventional proposals include techniques which comprise cutting the tip end of a scallop by a cutter or the like to creat an opening in the tip end of the scallop, and inserting an edged tool into the scallop through the opening, while allowing the edged tool to slide on an inner surface of one of shells of the scallop, thereby cutting the shell connected portion of the ligament closing the two shells to open the shells (i.e., open the shell mouth), for example, as described in Japenese Patent Application Laid-open No.87937/88 (which corresponds to Japanese Patent Publication No.14014/90).
There are also other conventionally know techniques which comprise opening the shell by heating a scallop by a heating means and then separting an adductor muscle from the other shell, for example, as disclosed in Japanese Patent Application Laid-open Nos.3899/75, 13900/77 and 3751/93.
In the above-described known technique which cuts the tip end of the scallop by the cutter, however, the ligament as the edible parts can be removed from the shell in the raw state used for raw eating, but this technique is accompanied by a problem that a great deal of labour and a lot of time are required in post-treatments for removing a ligament damaged due to the deposition of cuts on the ligament, and for removing the cuts from the ligament and the like. Further, the separation of the ligament from the shell is conducted by a manual operation for cutting a connected part of the ligament to the shell and the like, resulting in a problem that a great deal of labour is required for separting the adductor muscle from the shell, and it may be failed to effectively separate the ligament of the scallop in a raw state from the shell.
In the conventional technique which heats the shell by the heating means to open the shell, the shell mouth can be easily opened, but the surface of the ligament, particularly, the surface of the ligament located at the heated side is discolored into white to produce a so-called boiled state, resulting in a reduced quality in appearance. Thus, the quality suitable for raw eating cannot be maintained in many cases. In other words, the conventional technique using the heating means is accompanied by a problem that only a small amount of the ligament removed from the scallop can be supplied for raw eating. In addition, the separation of ligament from the shell after the opening of the shell is conducted by a manual operation and hence, is accompanied by a problem that a great deal of labour is required for separting from the ligament from the shell, and the ligament cannot be effectively separated from the shell.
Further, if the ligament is separated from the shall after being opened, using the knife-like tool referred to as the shell opener, the following problem is encountered: the connected portion of the ligament to the shell is cut even if any of the manual operation and a mechanical operation using an automatic machine is used. Therefore, the separated ligament has a jagged surface, resulting in a reduced quality in appearance. Even if the point of the knife-like tool is moved along the unevenness of the shell, the point cannot follow the unevenness of the shell and thus, a portion of the ligament remains on the unevenness of the shell, resulting in a reduced yield.
Further, the ligament separated from the shell by cutting the connected postion of the ligament to the shell is liable to absorb water through the cut surface. Therefore, the following problems: water used for trimming the ligament after being separated from the shell (as used herein, the term "trimming" means a scrubing for removing deposits such as fine internal organs dseposited on the ligament to provide an edible food product) is absorbed into the ligament, resulting in a reduced taste; and when the ligament has been preserved in a frozen state, delicious components flow out together with the water referred to as a drip, when the frozen ligament is thawed.
Therefore, a technique has been required which is capable of efficiently separating the ligament from the shell in a state in which a quantity suitable for raw eating is maintained.